The present invention relates to improvements in apparatus for controlling a load by means of a photodetector. More particularly, the invention relates to improvements in apparatus wherein a pushbutton, a knob or another suitable actuator can constitute an optomechanical transducer which initiates necessary changes in the condition of a load operating circuit.
Apparatus of the above outlined character are disclosed in the aforementioned commonly owned U.S. Pat. No. 4,591,712 to Thalmann as well as in U.S. Pat. No. 4,315,147 granted Feb. 9, 1982 to Alan L. Harmer for "Photoelectric switch with visible signal". The switch of Harmer employs two light sources one of which cooperates with a photodetector serving to change the condition of the load operating circuit. The purpose of the other light source is to illuminate a dial on the depressible portion of the actuator so that the person in charge can ascertain the condition of the load operating circuit. The depressible portion of the actuator carries a mirror which reflects infrared light but does not obstruct the passage of visible light. A drawback of the apparatus of Harmer is that it must employ a source of infrared light which is transmitted to the photodetector when the latter is to activate the load operating circuit, whereas the means for displaying the condition of the load operating circuit (and hence the condition of the load) must cooperate with a source of visible light. Thus, the wavelength of light which is used to activate the photodetector is substantially different from the wavelength of visible light, i.e., the damping action of the light conducting means upon one type of light is quite different from that upon the light of the other type. Consequently, the length of the light conductor means must be selected as a function of the less satisfactory damping action which, in turn, limits the length of the light conductor means. Were the apparatus of Harmer to employ two sources of visible light, the condition of the load operating circuit (i.e., the two positions of the depressible portions of the actuator) would be indicated by light having different hues which would be confusing to the operator.